The overall goal of this proposal is to develop and implement faster and more accurate synchrotron-based X-ray fluorescence computed tomography (XFCT) methods for the mapping of trace metals in biological samples. Many endogenous metals play critical roles in signal transduction and reaction catalysis, while others are quite toxic even in trace quantities. The study of these metals in biology would benefit greatly from the 3D spatially resolved maps of trace element distribution provided by the methods being explored in the proposal. In addition, exogenous metals are often critical components of new in-vivo molecular imaging agents. The techniques proposed here would provide calibration and subcellular localization information critical for the continued advancement of these technologies. XFCT is a stimulated emission tomography (ET) method in which monochromatic synchrotron X-rays are used to stimulate emission of characteristic X-rays from a sample, and it has the ability to produce three-dimensional maps of the distribution of individual elements in a small, intact specimen. As practiced now, the principal limitation of XFCT is its long acquisition time (on the order of 1 or more hours per slice), which limits the ability to image multiple samples for sake of comparison and improved experimental statistics. The key motivation for this proposed effort is to develop a novel detection system for XFCT studies that has a greatly improved imaging speed (10 to 100 times faster) while maintain a reasonable imaging resolution and an excellent sensitivity to the trace elements of interest. The specific aims of the proposal are: 1. To develop an ET-based detection system for XFCT applications. 2. To develop novel XFCT image reconstruction strategies accounting for secondary and scatter-induced fluorescence and that allow for region of interest imaging 3. To test the system and algorithms developed on a problem of biological interest: determining the spatial distribution of manganese introduced in islet cells Upon completion, this project will provide a validated means to perform trace metal imaging in biological specimens at significantly higher throughput than currently achievable. The project will also provide a foundation for scaling the techniques up to in vivo trace metal imaging in animals and humans. PUBLIC HEALTH RELEVANCE: XFCT is a stimulated emission tomography (ET) method in which monochromatic synchrotron X-rays are used to stimulate emission of characteristic X-rays from a sample, and it has the ability to produce three-dimensional maps of the distribution of individual elements in a small, intact specimen. As practiced now, the principal limitation of XFCT is its long acquisition time (on the order of 1 or more hours per slice), which limits the ability to image multiple samples for sake of comparison and improved experimental statistics. The overall goal of this proposal is to develop and implement faster and more accurate synchrotron-based X-ray fluorescence computed tomography (XFCT) methods for the mapping of trace metals in biological samples. Many endogenous metals play critical roles in signal transduction and reaction catalysis, while others are quite toxic even in trace quantities. The study of these metals in biology would benefit greatly from the 3D spatially resolved maps of trace element distribution provided by the methods being explored in the proposal. In addition, exogenous metals are often critical components of new in-vivo molecular imaging agents. The techniques proposed here would provide calibration and subcellular localization information critical for the continued advancement of these technologies.